1. Field of the Invention
The present invention relates to an extruder for formation of ceramic formed bodies, and more particularly, it relates to an extruder which can extrude and form large sized ceramic formed bodies having a large size.
2. Description of the Related Art
A ceramic honeycomb structure for use as a catalyst carrier, a filter or the like to purify an exhaust gas is manufactured through steps of extrusion, drying and firing, and thus a large sized ceramic honeycomb structure is requested for the purpose of purifying an exhaust gas from a large vehicle, a construction machine, a ship or the like.
The extrusion of laterally enlarged honeycomb formed bodies is accompanied with the problem that the honeycomb formed bodies are deformed due to their own weight. Therefore, the extrusion of the large sized honeycomb formed bodies is performed in a downward direction (the gravity direction).
In Patent Documents 1 and 2, an extrusion forming method of a ceramic formed body in a downward direction is disclosed. Moreover, in Patent Document 3, there is disclosed an extrusion forming machine in which a two-stages screw type extrusion forming machine is provided with a plunger type extruder. A kneaded material which is kneaded by the two-stages screw type extrusion forming machine is extruded in the downward direction by the plunger type extruder. Furthermore, in Patent Document 4, a vertical extruder including a screw is disclosed.    [Patent Document 1] JP-A-S63-230304    [Patent Document 2] JP-A-2003-311726    [Patent Document 3] JP-A-H07-32335    [Patent Document 4] JP-A-2010-105165
In Patent Documents 1 and 2, a raw material is formed into a kneaded material having a predetermined shape (the columnar shape) by use of a clay kneader, and the kneaded material is put in a forming machine, to extrude and form honeycomb formed bodies. There has been the problem that when the kneaded material having the predetermined shape is intermittently put in the forming machine and several honeycomb formed bodies are extruded from the one kneaded material having the predetermined shape, at a joint (change) portion between the one columnar kneaded material and another kneaded material, the surface of the honeycomb formed body becomes rough and a suitable honeycomb formed body cannot be obtained.
A forming device of Patent Document 3 has a stop time due to an intermittent operation of a plunger, and has a poor efficiency. Moreover, this forming device has the problem that a quality of the formed body (especially, the state of an outer peripheral portion) is poor at re-extrusion after the stop of the plunger. A forming device of Patent Document 4 has a three-stages screw constitution, and has the problem that a device constitution is complicated and increases cost.
An object of the present invention is to provide an extruder which decreases waste of a material or forming time, and extrudes and forms ceramic formed bodies having a suitable quality in the extrusion of large sized ceramic formed bodies.